The present invention relates, in general, to the field of integrated circuit devices and processes for manufacturing the same. More particularly, the present invention relates to an integrated circuit shielding technique utilizing stacked die technology incorporating top and bottom nickel-iron alloy shields having a low coefficient of thermal expansion of especial utility in conjunction with magnetoresistive random access memory (MRAM) and other devices requiring magnetic shielding.
Aeroflex Colorado Springs, assignee of the present invention, is a supplier of Qualified Manufacturers List (QML) MRAM products for high reliability aerospace applications including radiation hardened MRAM die in conjunction with the development of hermetic package technology required to assemble MRAM die into QML qualified packages.
Data in MRAM devices is not stored as an electric charge, as is the case with dynamic random access memory (DRAM) devices, but through the use of bits comprising magnetic tunnel junctions (MTJ). MTJ MRAM is made up of magnetic storage elements comprising a pair of magnetic layers separated by an oxide tunnel barrier, each of which can hold a magnetic field. In operation, one of the magnetic layers is set to a given polarity while the other's field can be changed to that of an external field to store data. Since MRAM data bits can be switched in response to magnetic fields on the order of 5 gauss, they are inherently sensitive to stray magnetic fields which can deleteriously impact performance if the device is left unshielded.